Surgical universal positioning block and tool guide

ABSTRACT

A positioning block for use in knee surgery includes a rotational mounting removably engageable to the bone element by a multi-axial fastener such that the mounting element is selectively rotatable relative to the bone element about at least two substantially perpendicular axes of rotation. A guide body portion is engaged with the rotational mounting element such that it is translatable relative thereto along while being rotationally fixed relative to the mounting element. The guide body portion is moveable relative to the bone element in at least three degrees of freedom, the three degrees of freedom including at least two rotational degrees of freedom and at least one translational degree of freedom. A trackable member on the guide body portion is identified and tracked by a computer assisted surgery system.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/062,737 filed Feb. 23, 2005 now U.S. Pat. No. 7,736,368which is itself a continuation of International Patent ApplicationSerial No. PCT/CA03/01307 filed Aug. 25, 2003, which claims priority on:US Provisional Application No. 60/405,353, filed on Aug. 23, 2002;

FIELD OF THE INVENTION

The present invention relates generally to a surgical tool for use inknee surgery. More particularly, the present invention is directed to amultiple degree-of-freedom positioning reference block and a surgicaltool guide, for use in computer assisted surgery (CAS) total kneereplacement.

BACKGROUND OF THE INVENTION

Accuracy of cuts and drilled holes is important in knee arthroplasty,wherein installation of the implants such that the kinematics of thenatural knee are duplicated as much as possible, is important to thesuccess of the total knee replacement. To achieve this, the use of CASsystems for orthopedic operations in general, and for total kneereplacement surgery in particular, is becoming increasingly morecommonplace with advancements in CAS equipment that ensure improvedaccuracy, fail safe operation and increasing ease of use.

Known camera based CAS system employ passive and active trackableelements affixed to objects, such as surgical tools and patient bonereferences, in order to permit the determination of position andorientation of the objects in three-dimensional space. Preoperativelytaken images or computer generated models created from preoperativepatient scans, are used to provide accurate patient anatomicalinformation to which the real-time position of the same anatomicalelements can be registered or calibrated, thereby permitting subsequenttracking of the anatomical elements and display of these elementsrelative to the surgical tools used during the surgery.

Total knee replacement surgery requires several precise cuts to be madein the femur and tibia, such that the implant fits correctly and bestreplicates the geometry of a natural healthy knee. To perform thesesteps, in both conventional and CAS total knee replacement, it is wellknow to use a guide block which provides a drill and/or cutting guide toassist the surgeon to perform the steps required to prepare the femurand tibia for receiving the implant.

In order to best understand the improvement the present inventionprovides over such guide blocks of the prior art, it is necessary tounderstand the steps performed during a typical total knee replacementsurgery to prepare the bones for receiving the implants.

The typical method steps used to prepare the femur for a kneereplacement implant, outlined below as an example, generally include:fastening a guide block on the femur, generally located by anintramedullary pin or screw inserted into the distal end of the femurand locating the guide block in the desired position; aligning a distalcutting guide, whether being integral with the guide block or a separateelement fastenable thereto, in a predetermined location relative to theguide block reference position and inserting locating pins through thedistal cutting guide and into the femoral condyles to fasten the cuttingguide in place on the anterior surface of the distal end of the femur;removing the distally mounted guide block, leaving the distal cuttingguide pinned to the anterior surface of the femur; making the distal cutto resect the predetermined amount of bone from the distal end of thecondyles; positioning the guide block freely on the newly cut distalsurface of the femur and ensuring that the resection level for theanterior cut, the anterior-posterior adjustment for implant sizing, therotational alignment and medial-lateral position of the positioningblock are all correct before fixing the guide block in place with pins;removing the positioning guide block, putting the peg hole drill guideblock onto the pins, and drilling the implant peg holes; and using thesepeg holes to install an anterior-posterior cutting block which is thenused to perform the anterior cut, and subsequently to install anappropriately sized chamfer cutting block which is then used to make theanterior-posterior chamfer and notch cuts.

The steps required to prepare the tibia are less involved. Generally,they include: aligning the mechanical axis of the tibia; obtainingproper rotational alignment of the guide block, and fastening it inplace to the anterior surface of the proximal end of the tibia;adjusting the guide block to ensure the desired posterior slope andlevel of tibial resection are provided; inserting location pins usingthe guide block; removing the guide block and replacing it with a tibialresection cutting guide that is retained in place with the locationpins; and resecting the chosen amount of tibial bone.

The above surgical procedures remain generally similar whethertraditional or computer assisted surgery is being performed. As such,the use of a cutting/drill positioning block having a positionidentifying member fastened thereto and trackable by a camera based CASsystem, for example, is known for use in total knee replacement surgery.However, while such tracked femoral positioning guide blocks providesignificant advantages over traditional non-CAS instruments, therenevertheless remains room for improvements to the current guide blocksused in total knee replacement surgery, whether being a guide block foruse with an image guided CAS system or traditional non-computer aidedsurgery, in order to further simplify surgical procedures and to enhanceaccuracy.

As discussed above, known total knee replacement procedures includecreating a distal on the femur in order to resect enough bone to permitthe installation of the femoral implant. In conventional, or noncomputer assisted, total knee replacement surgery a distal cutting blockis positioned and aligned by the surgeon and pinned in place on theanterior surface of the femur such that the cutting slot is aligned inthe correct location for the distal cut. In CAS total knee replacement,it is also known to use a distal pin drill guide to accurately createthe pin holes into which locating pins are inserted and employed to fixthe distal cutting guide, either integrally formed with the distal pindrill guide or being a separate element, in the correct location to makethe distal cut in the femur. Generally, the distal drill/cutting guidemember comprises part of an assembly including an anterior guidingplatform, that is fixed relative to the femur and on which thedrill/cutting guide is displaceable by a selected, measurable amount tolocate the drill/cutting guide in a desired position relative to theanterior guiding platform and therefore relative to the distal end ofthe femur. A tracked guide block is often intramedullarly fastened tothe femur, and the anterior guiding platform can then be engagedthereto. Depending on the type of implant being used, and once alignedwith the most distal femoral condyle, the drill/cutting guide can thenbe proximally displaced on the fixed anterior guiding platform by aselected amount corresponding to the amount of bone to be resected.

A captive spring loaded plunger, located within the distal drill/cuttingguide, is known to comprise a pointed pawl portion, which engages aseries of notches located on the anterior guiding platform to fix thedistal drill/cutting guide in place thereon. Demarcations on the guidingplatform indicate resection distance, and the spring loaded plunger canbe depressed to release the pawl from the notches and consequentlypermit movement of the drill/cutting guide along the guiding platform.As the notches are formed such that the distance between each notchaccurately corresponds to a single unit of distance, for example 2 mm, aprecise resection distance can be achieved by depressing thespring-loaded plunger and sliding the guide on the fixed platform therequired number of notches. Demarcations on the platform provide avisual indication of the position of the guide block position.

This spring loaded mechanism is effective to permit displacement of thedrill/cutting guide when required and to fix the guide in place when theguide is correctly aligned by releasing the outwardly biased plunger.However, such currently known mechanisms generally use a blind holewhich receives a helical spring and the plunger therein, the plungerbeing permanently retained within the guide. This often causessterilization problems, as cleaning the spring and inside bore of themechanism becomes difficult because the captive plunger can not beremoved. As a result, bacteria can build up inside the bore, and can notbe easily cleaned out and sterilized. This becomes a major problem ascleanliness is paramount in surgical environments.

As CAS systems permit improved visualization of the positioning blockrelative to the bone elements of the femur and projected reference blockaxes superimposed relative to those of the bone element, fewer fixedanatomical reference surfaces need to be used in conjunction withtracked CAS positioning reference blocks. However, to best permittemporary fixation block in a determined position, the reference blockrequires controllable adjustment of several degrees of freedom. Whilecertain flexibility is provided by total knee replacement positioningguide blocks of the prior art, there nevertheless remains a need for amore universal positioning block permitting additional controllableflexibility of movement, and being adapted for use with a CAS system.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide apositioning block for total knee replacement surgery having improvedmobility.

It is another object of the present invention to provide a positioningblock permitting proximal-distal adjustment when engaged with the distalend of the femur.

It is another object of the present invention to provide an improveddistal drill and/or cutting guide for use in total knee replacementsurgery, being adaptable to different implant types and capable ofsimplified location of the distal cut reference.

It is another object of the present invention to provide a surgical toolguide having a biased pawl mechanism that can be easily dismantled forcleaning.

There is therefore provided, in accordance with the present invention, amethod of installing a surgical positioning block on a bone element, thepositioning block having a reference surface and being operativelyengageable with a cutting tool, the method comprising: fastening thepositioning block to the bone element; determining a desired position ofthe reference surface of the positioning block relative to the boneelement; adjusting at least one of the position and orientation of thepositioning block, until the reference surface is in the desiredposition; and using the reference surface in the desired position as areference for locating the cutting tool in a predetermined location onthe bone element, such that a cut can be made in the bone element at thepredetermined location.

In accordance with the present invention there is also provided apositioning block for use in total knee replacement surgery, permittingfive degrees-of-freedom movement relative to a bone element to which itis fixed, the positioning block comprising: a rotational mountingelement being removably engageable to the bone element such that themounting element is selectively rotatable relative to the bone element,about three substantially perpendicular axes of rotation; and apositioning body portion being engaged with the mounting element suchthat it is translatable relative thereto along a proximal-distal axisand an anterior-posterior axis, while being rotationally fixed relativeto the mounting element such that the positioning body portion and themounting element rotate together relative to the bone element.

There is also provided, in accordance with the present invention, acomputer assisted total knee replacement surgery system comprising: apositioning block being fastenable to a bone element; means fordetermining the position and orientation of the positioning blockrelative to the bone element; the positioning block having a referencesurface and being operatively engageable with a cutting tool; means foridentifying a desired position of the positioning block relative to thebone element, such that the reference surface is located in a positionrelative to the bone element whereby the cutting tool, disposed in aknown position relative to the reference surface, is located in aselected position relative to the bone element, such that a cut can bemade in the bone element at the selected position; and a display capableof indicating when the desired position of the positioning block isreached.

There is further provided, in accordance with the present invention, asurgical positioning block permitting at least two independentlyadjustable degrees-of-freedom relative to a bone element to which it isengaged, the positioning block comprising: a positioning body beingoperatively engageable with a cutting tool and including a referencesurface, the positioning body being engageable to the bone element suchthat independent movement in at least two degrees-of-freedom relativethereto is selectively possible for adjustment purposes; and thepositioning body comprising at least two independent adjustmentmechanisms, each adjustment mechanism being adjustable in isolation forrespectively displacing the positioning block in one of said at leasttwo degrees-of-freedom, such that the reference surface can be locatedin a desired position and used as a reference to position the cuttingtool in a predetermined location for making a cut in the bone element.

There is also provided, in accordance with the present invention, asurgical instrument comprising: a first member and a second member beingslidingly displaceable relative to one another, the first member havingone of a rack and a pawl of a rack and pawl mechanism, and the secondmember having the other of the rack and the pawl; an elasticallydeflectable blade spring, the blade spring biasing one of the rack andthe pawl such that they are normally engaged together; whereby the firstand second members are slidingly displaceable relative to each otherwhen the rack and pawl are disengaged, and fixed relative to each otherwhen the rack and pawl are in engagement; and the first and secondmembers having substantially seamless surfaces that are at least one ofsubstantially exposed and exposable, such that the surfaces can easilybe pressure cleaned and autoclaved to remove biological mattertherefrom.

There is also provided, in accordance with the present invention, asurgical tool guide for preparing the femoral portion of a knee in atotal knee replacement surgery, comprising: a guide block having atleast one of a drill guide hole and a distal cutting guide slot, andcomprising an elastically deflectable blade spring; an anteriorlymounted platform, comprising a toothed rack and providing support forthe guide block such that proximal-distal sliding displacement of theguide block thereon is permitted; the platform being adapted formounting to a femoral reference positioning guide member distallyfastened to the femur; the guide block and the platform havingsubstantially seamless surfaces that are at least one of substantiallyexposed or exposable, such that the surfaces can easily be pressurecleaned and autoclaved to remove biological matter therefrom; and a pawlbeing normally biased by the blade spring such that it is in engagementwith the toothed rack on the platform; whereby the guide block isdisplaceable relative to the platform when the biased pawl is disengagedfrom the toothed rack and fixed relative thereto when the pawl isengaged with the toothed rack.

There is further provided a positioning block for use in knee surgerycomprising: a rotational mounting element being removably engageable tothe bone element by a multi-axial fastener such that the mountingelement is selectively rotatable relative to the bone element about atleast two substantially perpendicular axes of rotation; a guide bodyportion being engaged with the rotational mounting element such that itis translatable relative thereto along at least a proximal-distal axis,while being rotationally fixed relative to the mounting element suchthat the guide body portion and the mounting element rotate togetherrelative to the bone element, and wherein the guide body portion isthereby moveable relative to the bone element in at least three degreesof freedom, the three degrees of freedom including at least tworotational degrees of freedom and at least one translational degree offreedom; and a trackable member fastened to the guide body portion, thetracking member being identified and tracked in three dimensional spaceby a computer assisted surgical system such as to determine at least anorientation and movement of the guide body portion in three dimensionalspace.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention will become better understood with regard to the followingdescription and accompanying drawings wherein:

FIG. 1 is an exploded perspective view of a trackable CAS universalpositioning reference block according to the present invention;

FIG. 2 is a front elevation view of the universal positioning referenceblock of FIG. 1;

FIG. 3 is a side elevation view of a polyaxial mounting screw elementused to fasten the universal positioning reference block of FIG. 2 to abone element;

FIG. 4 a is a side elevation view of the universal positioning referenceblock of the present invention mounted to a femur;

FIG. 4 b is a side elevation view of the universal positioning referenceblock of the present invention mounted to a femur and the positioningbody proximally displaced such that it abuts the femur;

FIG. 5 a is a perspective view of the CAS universal positioning block ofthe present invention assembled with a distal drill/cutting guide block;

FIG. 5 b is a perspective view of the CAS universal positioning block ofthe present invention assembled with an alternate cutting guide block;

FIG. 6 is a perspective view of the universal positioning block of FIG.2 with a calibration instrument engaged thereto;

FIG. 7 is a perspective view of an alternate embodiment of a trackableCAS universal positioning block according to the present invention foruse in total knee replacement surgery;

FIG. 8 is a cross-sectional view taken through line 8-8 of FIG. 7;

FIG. 9 is a perspective view of a tibial polyaxial screw drill guide foruse with the present invention;

FIG. 10 a is a side elevation view of the universal positioning block ofFIG. 7, used in conjunction with tibial posterior slope matchingalignment pins;

FIG. 10 b is a side elevation view of the universal positioning block ofFIG. 7, used in conjunction with a tibial positioning stylus;

FIG. 11 a is a front elevation view of the polyaxial screw alternatelymounted in the tibia;

FIG. 11 b is a side elevation view of the universal positioning block ofFIG. 7, alternately mounted on the polyaxial screw of FIG. 11 a;

FIG. 12 is a schematic flow chart of the method used to install theuniversal positioning block of the present invention to a bone element;

FIG. 13 is a perspective view of an automatic calibrator adaptor for usewith the universal positioning block of the present invention;

FIG. 14 is a perspective view of the automatic calibrator adaptor ofFIG. 13 assembled with the universal positioning block and thecalibration instrument of FIG. 6;

FIG. 15 is an exploded perspective view of the distal drill/cuttingguide block of FIG. 5 a;

FIG. 16 a is a top elevation view of the surgical tool guide as shown inFIG. 15, wherein the position locking mechanism is engaged, therebyfixing the guide block in place on the guiding platform;

FIG. 16 b is a top elevation view of the surgical tool guide as shown inFIG. 15, wherein the position locking mechanism is released, therebypermitting movement of the guide block on the guiding platform;

FIG. 17 a is a perspective view of the distal drill/cutting guide blockas shown in FIG. 15 with the plunger engaged therein;

FIG. 17 b is a side elevation view of the plunger of FIG. 17 a;

FIG. 17 c is a front elevation view of the tool guide of FIG. 17 a;

FIG. 18 is an exploded perspective view of the distal drill/cuttingguide block of FIG. 15 and the CAS universal positioning reference blockof FIG. 1;

FIG. 19 is a perspective view of a universal distal cutting guideadaptor mounted on the universal positioning block and being used tolocate a standard distal cutting guide block;

FIG. 20 a is a perspective view of a universal anterior cutting guideadaptor mounted on the universal positioning block; and

FIG. 20 b is a perspective view of the universal anterior cutting guideadapter of FIG. 20 a pined in place on the femur and being used tolocate a standard anterior cutting guide block.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Throughout this application, the preferred embodiment of the presentinvention will be referred to as a universal positioning block or simplypositioning block, and is preferably for use in total knee replacementsurgery and is adapted to accurately position and align a cutting tool.The universal positioning block comprises a guide body or cutting toolguide element that is operatively engageable with a cutting tool,whether directly by providing a cutting guide surface on the cuttingtool guide element itself or by being engageable with a separate cuttingguide block which is used to guide the cutting tool. It is to beunderstood that such a cutting tool as defined herein includes allinstruments which can remove bone from a bone element, such as drillsand saws for example, and that such a cutting tool guide element orsurface thereon is similarly adapted for guiding any instrument whichcan remove bone from a bone element such as a drill bit or a saw blade.

Preferably, the universal positioning block is trackable by a computerassisted surgical (CAS) system which provides means for determining theposition, orientation and movement of the universal positioning block inthree dimensional space, and permits the positioning block to bevisualized relative to the patient anatomy. The CAS system furtherprovides means for determining a desired position of the universalpositioning block relative to a bone element, whether from a realpatient, a cadaver or a model. The CAS system further provides means forindicating where to fasten the universal positioning block on such abone element such that it can be adjusted into the desired position.However, the present universal positioning block can equivalently beused in conventional, or non-computer assisted, surgical applications.Additionally, the present universal positioning block can be used withboth CT-based and CT-less CAS systems. The CAS system can, in otherwords, use either computer generated anatomical models created frompre-operatively taken scans, such as CT scans, or use intra-operativelygenerated bone surface models created by digitizing a plurality ofpoints and anatomic landmarks on the surface of the bone element, torelate the position of the universal positioning block to the boneelements of the patient.

Referring to FIG. 1, the universal positioning block assembly 10comprises generally a cutting tool guide element or guide body member12, a mounting member 14 and a tracker member 16. The tracker member 16comprises at least three detectable elements 17, engaged to thetrackable member via mounting posts 15. The detectable elements 17 arepreferably spherical passive markers locatable by a camera-based,optical tracking CAS system. However, it is to be understood that activeoptical markers can equivalently be used as the detectable elements, andthat CAS systems using electromagnetically and acoustically detectableelements can also similarly be employed. The main guide body 12comprises a large central aperture 18 for receiving the mounting member14 therein. The guide body 12 comprises cutting guide surfaces, such asthe two drill guide holes 36, which extend through the guide body 12.The guide body 12 also includes means for engagement to a cutting guide,comprising, for example, a pair of mounting points 38 having peg holes40 are disposed on the top of the guide body, permitting engagement withanother drill/cutting guide block for example. The mounting member 14comprises a translation mechanism including a fastener receiving mountelement 24, which slides within the central guide slot 22 disposedwithin the mounting member body 20. The fastener mount element 24comprises a semi-spherically shaped bowl 26 which has a through hole atthe bottom thereof. The fastener mount element 24 is displaced relativeto the mounting member body 20 by an endless screw 28, engaged to thefastener mount element and extending through an inside-threaded hole 32in the mounting member body 20. The translation screw 28 is actuated bya screw head 30, such that rotation of the screw head 30 causes thefastener mount element 24 to be translated within the central guide slot22. The translation, or elevation, screw 28 thereby enables the entirepositioning block to be raised or lowered along an anterior-posterioraxis when engaged to a distal end of a femur. The entire mounting member14 additionally slides within the central aperture 18 of the guide body12, generally permitting the guide body to be displaced along aproximal-distal axis when the positioning block is engaged to a distalend of a femur. A friction locking screw 34 extends through the side ofthe guide body and engages the mounting member 14, such that it can beretained in a selected position relative to the guide body 12.

The universal positioning block 10 is shown assembled in FIG. 2, howeverwith the trackable member 16 alternately mounted, via the tracker stem19 pivotable about pivot 21, on the opposite side of the guide body 12.A locking screw 23 is preferably used to fix the trackable member 16 inplace on the selected side of the universal positioning block 10. Thetrackable member can be fixed in position on the guide body, orremovably engaged to either side of the guide body of the positioningblock, such that the best visual contact between the detectable elementsand the cameras of the CAS system is ensured. For example, if thetrackable member is removably engageable, it can be switched sides ofthe guide body depending on which knee is being operated on, therebyreducing the need to displace the cameras or other equipment of theimage guided surgery system. A removably lockable quick release canalternately be used in place of the fixed pivot 21 and the locking screwfastener 23, to retain the stem 19 in place within the guide body 12,such that no movement of the trackable member 16 relative to the guidebody is permitted, while nevertheless permitting removal to the stemfrom the guide body when required.

As best seen in FIG. 6, the guide body 12 also preferably comprises asocket disposed in an underside edge and a releasable retention member42. The socket is adapted to receive an automatic calibration instrument44, comprising another set of detectable elements thereon. Thecalibration instrument 44, which is permanently calibrated, permitscalibration of the tracked positioning block, such that by securelyengaging it with the tracked positioning block the position andorientation in space of the detectable elements 17 of the trackablemember 16 are determined relative to similar detectable elements of theremovable calibration instrument 44, which are themselves in a knownposition in space. The position and orientation of the positioning block10 can therefore be calibrated, such that the image guided surgicalsystem can accurately track it in three dimensional space. The automaticcalibration instrument 44 preferably snaps into engagement with theguide body 12 of the positioning guide block. An alignment pin 46located on the calibration instrument fits into a corresponding notch 49in the guide body, to ensure that the calibration instrument 44 iscorrectly oriented relative to the positioning guide block. The biasedretention member 42 on the positioning block engages the calibrationinstrument 44 via the alignment pin 46, thereby securely retaining thecalibration instrument within the mating socket of the guide block whilethe calibration procedure is performed. Once completed, the leverportion of the releasable retention member 42 is actuated, therebyreleasing the portion of the retention member in contact with thealignment pin 46 of the calibration instrument and permitting thecalibration instrument 44 to be disconnected from the positioning block.Alternate retention members can equivalently be used. For example, asseen in FIG. 5 b, a friction screw retention member 48 is similarly usedto selectively retain the calibration instrument connected with thepositioning block. Additionally, no retention member may be required ifthe calibration instrument can be engaged with the positioning block insuch a way that it is precisely located and cannot be easily displacedwhile the calibration process is being performed.

Referring to FIGS. 13 and 14, which depict an alternate method oftemporarily fastening the calibration instrument 44 to the universalpositioning block 10 using a separate automatic calibrator adaptor 265.Particularly, the automatic calibrator adaptor 265 comprises a generallycylindrical body 267 within which the calibration instrument 44 can beinserted via opening 269 at a first end thereof. Several grooves 271 areprovided to receive the alignment pin 46 of the calibration instrument44 therein. Integrally formed at a second of the body 267 is a positingblock engaging member 273, sized to fit within the central slot 22,122disposed within the mounting member body 20,120 of the positioning block10, 110. The positioning block engaging member 273 of the automaticcalibrator adaptor 265 can thus be inserted with the central slot 22,122and can be clamped therein by tightening the screw 28,128 to displacethe fastening receiving mount element 24,124 until it clamps thepositioning block engaging member 273 of the automatic calibratoradaptor 265 between the fastening receiving mount element 24,124 and thebase of the mounting member body 20,120. The flange 275 of the automaticcalibrator adaptor 265 preferably abuts a surface of the guide body12,112. The automatic calibrator adaptor 265 further comprises a screwhead 277 which rotates screw body 279 within the automatic calibratoradaptor 265, and is used to fasten the calibration instrument 44 withinthe automatic calibrator adaptor 265 by threaded mating engagement withan internally threaded socket in the calibration instrument 44. Theautomatic calibrator adaptor 265 therefore permits the universalpositioning block 10,110 and the calibration instrument 44 together in alocked position, such that the universal positioning block 10,110 can beeasily calibration when the three elements are fastened together andshown to the cameras of the computer assisted surgery system. As thecalibration instrument is always calibrated and hence in a knownposition, the relative position of the detectable elements 17 of theuniversal positioning block 10,110 to those of the calibrationinstrument 44 can be computed by the CAS system.

A polyaxial mounting screw 25, as best seen in FIG. 3, is used to mountthe universal positioning block 10 to the bone. The polyaxial screw 25comprises generally a main screw body 29 having threads on the outside,a shoulder portion 27, and a spherical screw head 31 having a pluralityof integrally formed individual petal elements 33. A central conicalscrew 35 is inserted through the center of the screw head, and whenengaged therein, forces the petal elements 33 outwards, thereby causingthem to press against the semi-spherical surface 26 of the fastenermount element 24. This consequently immobilizes the fastener mountelement 24 in position on the spherical polyaxial screw head 31, fixingit in position thereon. The petal elements 33 are slightly elasticallydeflectable and the polyaxial screw head 31 is sized such that the petalelements are forced slightly radially inward when the fastener mountingelement is pressed down overtop, and engaged to the screw head. Thisensure that once snapped in place, the fastener mount element 24, andsubsequently the entire positioning block assembly, can freely rotateabout the polyaxial screw head in three rotational degrees of freedom.Once the positioning block is aligned in the desired position, theconical screw 35 at the center of the polyaxial screw head 31 can betightened, thereby rotationally fixing the guide block assembly in placeon the polyaxial mounting screw 25. When the term polyaxial screw isused herein, it is to be understood that it comprises preferably a screwhaving a substantially spherical head. The spherical head permits a balland socket type joint to be created, when an element with a receivingsocket is engaged with the ball head of the polyaxial screw. Thespherical head preferably, but not necessarily, includes the individualpetal elements that are displaceable by the central conical screw inorder to provide a locking mechanism. Other mechanism to lock the memberwith the receiving socket in a selected position on the head of thescrew are equivalently possible.

Referring now to FIGS. 4 a and 4 b, showing the universal positioningblock assembly 10 mounted to the distal end of a femur 39 by thepolyaxial screw 25, and to FIG. 12 showing method steps involved withinstalling the positioning block on a bone element. The degree ofmobility of the universal positioning block 10 permits significantsimplification of the surgical procedures employed in certain surgeries,such as total knee replacement surgery. Generally, the first step 201comprises fastening the positioning block 10 to the bone element. Asshown in FIG. 4 a, this is preferably done using the polyaxial screw 25,which is first aligned with the entrance point of the mechanical axis atthe distal end of the femur and introduced therein until its shoulder 27touches the bone. The fastener mount element 24 of the universalpositioning block 10, as best seen in FIG. 1 and FIG. 2, is snapped ontothe head 31 of the polyaxial screw.

The step 203 of determining a desired position of the positioning block10, or a portion thereof such as a reference surface 45 on the guidebody 12, is done by either by the CAS system itself, by the surgeonusing the CAS system as a guide or independently by the surgeon, inorder to determine what final position the positioning block 10 shouldbe moved into in such that a drilled hole or a sawn cut can be made inthe bone element at a predetermined location that is required for theinstallation of an implant. Step 205 comprises adjusting the positionand orientation of the positioning block 10 until it, or a portionthereof such as the reference surface 45 of the guide body 12, islocated in the desired position that was previously determined in step203. This can involve rotatably adjusting the positioning block 10relative to the bone element, using the CAS system to aid in the correctorientation in each rotational axis of rotation. Three rotationaldegrees of freedom are thereby possible, and the entire positioningblock 10 can be oriented in a desired plane, for example parallel to thedistal cut to be made in the femur. Step 205 can also include proximallydisplacing the positioning block 10 in the direction 43 such that theproximal surface 45 is translated from a position shown in FIG. 4 a to aposition shown in FIG. 4 b, abutting the femur 39. As the head 31 of thepolyaxial screw 25 is distally spaced from the condyles 41 of the femur39, the positioning block 10 requires a reference point with respect tothe bone such that the location of the distal cutting guide, which willbe fixed to the positioning guide block, will correctly correspond tothe amount of bone which must be resected by the distal cut.

The proximal-distal translation of the guide block body 12 relative tothe mounting member 14 greatly simplifies the referencing of the guideblock with the femur. As the mounting member 14 is engaged in place onthe head of the polyaxial screw, it is fixed in a proximal-distaldirection relative to the bone. However, as the guide block body 12 canaxially slide relative to the central mounting member 14 when thelocking screw 34 is disengaged, the tracked guide body portion 12remains rotationally fixed relative to the mounting member but cantranslate in the proximal-distal direction 43. This permits the guidebody 12 to be proximally displaced until its proximal surface 45directly abuts the most distal end of the condyles 41, as shown in FIG.4 b. By tightening the locking screw 34, the guide body 20 is retainedin place on the central mounting member 14. The conical screw 33, asseen in FIG. 3, when tightened, fixes the positioning block 10 in placeon the head 31 of the polyaxial screw 25, thereby fixing the referencesurface 45 in the chosen desired position. The distal end of the femur,which is accurately located by the tracked guide body 20 that is locatedby the CAS system, can then be used as a reference plane, from which theresection depth can be easily measured. The amount of bone resectedoften varies as a function of the type of implant line being used, andthe specific structure of the patient anatomy.

Further adjustment is also possible with the present universalpositioning block assembly 10. Step 205 of FIG. 12 also comprisestranslation of the entire positioning block assembly 10 relative to thepolyaxial screw 25, and therefore relative to the femur, in theanterior-posterior direction 47. By rotating the screw head 30, themounting member body 20, shown in FIG. 2, and consequently the entireguide block body 12 are displaced relative to the fastener mount element24 that is fixed to the polyaxial screw head 31. This affordssubstantially vertical adjustment of the positioning block if requiredby the specific procedure or the anatomy of the patient being operated.The positioning block can therefore be adjusted in five degrees offreedom, namely rotation about three rotational axes and translationalong two perpendicular axes, namely in directions 43 and 47.

Once the desired position and orientation of the positioning block 10 isachieved, step 207 is performed, which comprises using the positioningblock 10, and more particularly the reference surface 45, to locate acutting tool, such as a drill or a saw, in a predetermined location, aknown distance away from the reference surface 45, in order to make ahole or cut in the bone element at the predetermined location, asrequired by the implant being installed.

The universal positioning block assembly 110 of FIGS. 7 and 8, issimilar to the guide block assembly 10, however comprises severaladditional features. Referring to FIG. 7 and FIG. 8, the universalpositioning block assembly 110 comprises generally a guide body 112, amounting member 114 and a tracker member 116. The tracker member 116 ispreferably engaged with the guide body 112 via a mounting stem 119 andcomprises at least three mounting posts 115 thereon for retainingtrackable elements which are locatable by the CAS system. The mountingmember 114 can translate relative to the guide body 112 within a centralaperture 118. The mounting member 114 is captive within the centralaperture 118, being retained therein by the closed end of the aperture118 at one end and by retention pins (not shown), which prevent thecomplete removal of the mounting member 114 at the opposing end of theslot comprising the central aperture 118. A locking screw 134 extendsthrough the guide body 112 for frictional engagement with a surface ofthe mounting member 114, for fixing the mounting member 114 in placesuch that relative movement between the mounting member 114 and theguide body 112 is substantially prevented. All individual parts of theuniversal positioning block assembly 110 are preferably retained captivewith the block guide body 112. This eliminates the possibility of anysmall pieces becoming detached during surgery or being lost should asmall part be dropped, for example. Drill guide holes 136 extendtransversely through the guide body 112, and a pair of peg holes 140 aredisposed on an upper surface of the guide body 112, permittingengagement with another drill/cutting guide block for example. Themounting member 114 comprises an independent adjustment mechanismincluding a fastener receiving mount element 124, which slides within acentral slot 122 disposed within the mounting member body 120, and istranslated therein by adjustment screw 128 which is manually actuatedvia screw head 130. The fastener receiving mount element 124 comprisesan aperture 126 for engaging the substantially spherical head of thepolyaxial screw 25.

As best seen in FIG. 8, the aperture 126 preferably includes opposedconcave recessed portions, comprising a first substantiallyfrusto-conical portion and a subsequent enlarged region capable ofreceiving the head of the polyaxial screw 25 therein. This permits thefastener receiving mount element 124 to be snapped into engagement withthe head of the polyaxial screw 25, such that the fastener receivingmount element 124 can be held in position but nevertheless can berotated relative to the polyaxial screw 25 without being fixed relativethereto. As described above, the guide body 112 can then be translatedrelative to the fastener receiving mount element 124 within the centralaperture 118. The guide body 112 is displaced along a proximal-distalaxis when the positioning block assembly 110 is engaged to a distal endof a femur. Friction locking screw 134 extends through the side of theguide body 112 and engages the mounting member 114, such that it can beretained in a selected position relative to the guide body 112. Thefastener mount element 124 is displaced relative to the mounting memberbody 120 by endless screw 128, engaged to the fastener mount element 124and extending through the mounting member body 120. The translationscrew 128 is actuated by a screw head 130, such that rotation of thescrew head 130 causes the fastener mount element 124 to be translatedwithin the guide slot 122. The translation, or elevation, screw 128thereby enables the entire positioning block guide body 112 to be raisedor lowered along an anterior-posterior axis when engaged to a distal endof a femur.

The universal positioning block assembly 110 further comprises at leasttwo independent adjustment mechanisms that are adjustable in substantialisolation for adjustably displacing the cutting tool guide element orguide body 112 in one of at least two degrees-of-freedom. Theindependent adjustment mechanisms preferably include two adjustmentscrews 171, adapted for adjustment of the Varus-Valgus angle. TheVarus-Valgus adjustment screws 171, best seen in FIG. 8, have outerthreads 181 for threaded engagement with holes 179 in the guide body 112and include substantially flat end faces 183 for pressed contact withthe bone surface, such as the distal ends of the femoral condyles forexample. The Varus-Valgus adjustment screws therefore permit fine tunedangular adjustment of the universal positioning block assembly 110relative to the bone element about a substantially vertical axis, whenthe universal positioning block assembly 110 is fastened to the distalend of the femur for example. This permits more accurate location of theuniversal positioning block assembly 110, in comparison with manualadjustment of the assembly until the correct Varus-Vargus angle isachieved. These adjustment screws therefore permit the universalpositioning block assembly 110 to be accurately adjusted on thepolyaxial screw in a single rotational degree of freedom, as guided bythe CAS system. This helps simplify the multiple-degree of freedomadjustment required to position the universal positioning block assembly110 in the desired final position.

The universal positioning block assembly 110 also comprises a posteriorcondyle palpator 163, which can be used to better centrally locate theuniversal positioning block assembly 110 when engaged to the polyaxialscrew 25 fastened to the distal end of the femur. The posterior condylepalpator 163 is generally L-shaped, being engageable to the positioningblock guide body 112 via mounting pins which engage corresponding holeswithin the outer face of the positioning block guide body 112, andhaving leg portions 165 extending generally away from the positioningblock guide body 112, in a proximal direction when the universalpositioning block assembly 110 is engaged to a distal end of a femur.The extending leg portions 165 include generally flat palpating regions169 for abutting the posterior surfaces of the femoral condyles. In thisway, the universal positioning block assembly 110 can be consistentlymounted on the femur such that it is substantially verticallypositioned. Ideally, the polyaxial screw 25 is vertically located atabout one third of the anterior-posterior distance from the anteriorsurface of the distal end of the femur, meaning the universalpositioning block assembly 110 will be ideally vertically located moreanteriorly than posteriorly on distal end of the femur. The exactlocation, however, will depend largely on the particular anatomy of eachpatient, which can greatly vary. This will increase the likelihood thatthe anterior-posterior adjustment range permitted by the translationscrew 128 will be sufficient. Additionally, with the leg portions 165 ofthe posterior condyle palpator 163 abutting the posterior condyles ofthe femur, a pivot point is temporarily created about the contactpoints. When the translation screw 128 is rotated, the entire guide body112 of the universal positioning block assembly 110 is translatedrelative to the mounting member 114 engaged with the polyaxial screw 25,and is therefore forced to pivot about a substantially horizontal axisdefined between the contact points between the generally flat palpatingregions 169 and the femoral condyles. This enables the controlledadjustment of the universal positioning block assembly 110 about asubstantially medial-laterally extending horizontal axis.

Therefore, both the posterior condyle palpator 163 and the Varus-Valgusadjustment screws 171 help permit the controlled and precise adjustmentof one rotational degree of freedom. This greatly simplifies theadjustment of the position and orientation of the universal positioningblock assembly 110 in space. Using the CAS system, each of therotational and translational degrees of freedom can be individuallyadjusted into a predetermined position or orientation, to achieve thedesired final position and orientation of the universal positioningblock assembly 110 relative to the bone element. The user can identifyto the CAS system what the desired final position and orientation of theuniversal positioning block assembly 110 relative to the bone elementshould be, and the CAS system can subsequently prompt the user to varyeach of the degrees of freedom independently as required.

The five degree of freedom adjustment that is possible by thepositioning block assembly 10,110 permits it to be universally used intotal knee replacement surgery, regardless of the type of implant linebeing used and of the surgical steps to be performed. It can be used,for example, in conjunction with a cutting guide to create the distalcut required for femoral implant preparation.

FIG. 5 a shows the universal positioning block 10 having a distal pindrill guide assembly 50 mounted thereto, which is more fully describedin U.S. Provisional Patent Application Ser. No. 60/405,353, filed Aug.23, 2002, the contents of which are incorporated herein by reference.The distal pin drill guide assembly 50 generally comprises an anteriorguiding platform 54 and a displaceable drill guide block 52. Theanterior guiding platform 54 includes locating pegs which mate with thepeg holes 40 in the two mounting points 38 of the positioning guide body12, and a proximally extending elongated tongue portion 80 on which thegrill guide block can slide. The drill guide block 52 is preferablysized such that when fully abutted against the anterior guiding platform54, the location of the pin drill holes 86 correspond to the locationrequired for the locating pins which are inserted into the femur tosecure the distal cutting guide block in the precise position such thatthe required amount of bone is resected by the distal cut. However, thedrill guide block 52 can be proximally displace along the anteriorguiding platform 54, and selectively fixed in position thereon. Knowingthe position of the positioning guide block 12, abutted with the distalend of the femur, the CAS system can indicate to the surgeon exactly howfar along the anterior guiding platform 54 the drill guide block 52 isto be displaced, such that the distal cutting guide pin holes 86 can beused to create drilled holes in the bone at the necessary position. TheCAS system can indicate this graphically, or indicate numerically howmany notches or graduations the drill guide block 52 is to be translatedalong the elongated tongue portion 80 of the guiding platform 54. Thesystem can also simply indicate at which final demarcation the drillguide block 52 is to be located, thus avoiding the surgeon having tocount the number of graduation or notches that the drill guide must bemoved by.

Alternately, as shown in FIG. 5 b, a conventional femoral distal cuttingguide block 59 can be engaged directly to the universal positioningblock 10, via an alternate tool guide guiding platform 55, whichsimilarly mates with the positioning block 10 and comprises proximallyextending mounting pegs 57, to which the cutting guide block 59 can bemounted. A thumb-screw 61 is provided to engage the cutting block 59,such that it can be pulled towards the proximal face of the universalpositioning block body 12, and positioned at the exact distance requiredfrom the proximal face of the positioning block 10 abutted to the distalend of the femur, which will correspond to the amount of condyleresected by the distal cut made using the cutting block 59 as a guide.

It is to be understood that the alternate universal positioning blockassembly 110 can similarly be used in conjunction with the distal pindrill guide assembly 50 and the conventional femoral distal cuttingguide block 59, as respectively shown in FIGS. 5 a and 5 b. It is to beunderstood that the alternate universal positioning block assembly 110can similarly be used in conjunction with the distal pin drill guideassembly 50 and the conventional femoral distal cutting guide block 59,as respectively shown in FIGS. 5 a and 5 b. While the positioning blockassembly 10 is shown without a trackable member 16 in FIG. 5 a, it is tobe understood that the universal positioning block assembly 10 ispreferably used in conjunction with an image guided computer assistedsurgical system, capable of locating the detectable elements 17 of thetrackable member 16, such as shown in FIG. 5 b, such that the positionand orientation of the universal positioning block can be determined anddisplayed by the CAS system relative to the anatomical structures of thepatient. However, the present universal positioning block 10,110 canequally be used in conventional non-computer assisted surgery, whereinthe five degrees of freedom adjustment of the universal positioningblock can similarly permit more precise alignment of surgical toolguides engaged to the positioning block assembly 10,110.

The drill guide holes 36 located in the guide body 12 of the positioningblock assembly 10,110 permit the femoral implant peg holes to be drilledin the distal end of the femur. As the proximal face 45 of thepositioning block 10 can be directly abutted against the most distalpoint of the condyles, the depth of the peg holes which must be drilledcan be calculated, knowing the distance to be resected by the distalcut. For example, if the peg holes are to be made 5 mm deep and 10 mm ofbone is to be resected by the distal cut, then 15 mm deep peg holes canbe drilled using the drill guide holes 36 before the distal cut is made.As selected additional anterior-posterior adjustment is possible ifrequired using the translation screw 28 of the mounting member 14, theimplant peg holes can be accurately aligned regardless of their positionrelative to the bone mounting screw. By enabling the proximally directedimplant peg holes to be drill before the distal cut is made, severalsurgical steps can be avoided, thereby significantly simplifying theprocedure required to perform total knee replacement surgery using a CASpositioning guide block. The posterior condyles palpator 163 of theuniversal positioning block assembly 110, may also aid in correctlylocating the position of the femoral implant peg holes which are drilledinto the distal end of the femur.

Although the universal positioning block assembly 10,110 has beendescribed above with emphasis on the preparation of the femur forreceiving the femoral portion of a knee replacement implant, theuniversal positioning block assembly 10,110 is also used for thepreparation of the tibia for the corresponding tibial portion of a kneereplacement implant. The steps required to prepare the tibia, include:defining the tibial mechanical axis; using the universal positioningblock assembly 10,110 to determine a desired rotational alignment of theguide block and fastening it in place to the anterior surface of theproximal end of the tibia using the polyaxial screw 25; adjusting theguide block to ensure a desired posterior slop and level of tibialresection; inserting location pins using the guide block; removing theguide block and replacing it with a tibial resection cutting guide thatis retained in place with the location pins; and resecting the chosenamount of tibial bone.

As correctly locating the entry point of the polyaxial screw into thetibia can be sometimes problematic and time consuming, the tibialpolyaxial screw drill guide 87, as shown in FIG. 9, is preferably usedto drill a pilot hole in the correct location for the polyaxial screwplacement. The tibial polyaxial screw drill guide 87 comprises a mainbody 89 and two locating pins 91 extending from an upper portion of themain body 89. A drill guide hole is disposed in the main body 89 at aspecified distance away from the locating pins 91. Each locating pin 91is adapted for resting on the proximal end of the tibia 93, on thetibial plateaus 100 on either side of the tibial tuberosity 95. The bit97 of the drill 99 can then be inserted through the drill guide hole 94in the main body 89, and a pilot hole for the polyaxial screw can beeasily created in the correct location in the tibia. As a general guide,the drill guide hole 94 in the main body 89 is preferably provided at aposition relative to the bottom of the locating pins 91, and therefromfrom the surface of the tibial plateau.

Referring now to FIG. 7 and FIG. 10 a, with regards the use of theuniversal positioning block assembly 110 for the preparation of thetibia 93 for the knee implant, the universal positioning block assembly110 comprises a pair of transversely extending alignment holes 188 thatextend transversely through the guide body 112. These alignment holes188 are used for matching the posterior slope of the tibial plateau withthe orientation of the universal positioning block assembly 110. Withthe universal positioning block assembly 110 engaged to the tibia 93 bythe polyaxial screw 25 such that the universal positioning blockassembly 110 can be rotated relative thereto, the two alignment pins 194are inserted into the alignment holes 188, as shown in FIG. 10 a. Thealignment pins 194 are used to rest on top of the sloped posteriortibial plateau 100 such that the posterior-anterior angle of theuniversal positioning block assembly 110 corresponds to the posteriorslope of the tibia.

The universal positioning block assembly 110 is further engageable withanother adjustment simplification device for use when using theuniversal positioning block assembly 110 with the tibia 93. As best seenin FIG. 7, the universal positioning block assembly 110 includes a pairof threaded, longitudinally extending positioning stylus engagementholes 196. As shown in FIG. 10 b, these engagement holes 196 are adaptedfor engaging a tibial positioning stylus 198 to the universalpositioning block assembly 110. The tibial positioning stylus 198,comprising an adjustable support member 202 and an elongated styluselement 204, is used to help locate the universal positioning blockassembly 110 in a desired position relative to a proximal end of thetibia 93, such as a tibial plateau 100.

Once all the necessary adjustments of the universal positioning blockassembly 110 are made and it is positioned as required relative to thetibia 93 using the CAS system and the abovementioned adjustment tools,the conical screw 35 of the polyaxial screw 25 is tightened, fixing theuniversal positioning block assembly 110 in place. The tibial cuttingguide pins holes can then be drilled in the tibia 93 using the necessaryguide holes 208 in the guide body 112, best seen in FIG. 7, and the pinscan be inserted through the guide holes 208 and into the tibia. Theentire universal positioning block assembly 110 can then be removed, anda tibial cutting guide block can be installed onto the pins, and thetibial cut can be made to resect the chosen amount from the proximal endof the tibia 93.

In an alternate technique for mounting the universal positioning blockassembly 110 to the tibia, the polyaxial screw 25 is inserted in theintercondylar tubercle 95 of the tibia 93, as seen in FIG. 11 a,parallel to the mechanical axis of the tibia. This is in contrast to theabove described method, as illustrated in FIGS. 10 a-10 b, where thepolyaxial screw is inserted into the tibia perpendicularly to the tibialmechanical axis, on an anterior surface thereof. Referring to FIG. 11 b,the universal positioning block assembly 110 can then be engaged to thepolyaxial screw 25 such that it is oriented substantially parallel tothe desired tibial cut to be made. This alternate mounting arrangementpermits the tibial cutting guide block 159, fixed to the universalpositioning block assembly 110 via a tibial cutting block support 185,to be pined directly to the tibia 93 without removal of the universalpositioning block assembly 110 and other CAS equipment. Particularly,the translating mounting member 114 of the universal positioning blockassembly 110, permits the guide body 112 to be lowered relative to thefixed polyaxial screw 25 such that the tibial cutting block 159 islowered to a desired resection level. Preferably, a spacer 206 is usedas shown in FIG. 11 b. Based on the dimensions of the tibial cuttingguide block support 185, the spacer 206 is sized such that the requireddistance “d”, between the deepest point of the tibial plateau 100 andthe resection cut to be made, corresponds to the distance between thespacer 206 and the cutting guide slot in the tibial cutting guide block159. This distance “d” is defined by the implant to be used. Forexample, when using Natural-Knee® II type implants, this distance shouldbe approximately 7 mm (about 0.276 inches).

In an alternate embodiment, the insertion of the polyaxial screw 25 intothe femur 39 or the tibia 93 can be done using a trackable screwdriver.The CAS system, knowing the position of the screwdriver and thereforethe polyaxial screw 25, can therefore determine the proximal-distalposition that the polyaxial screw 25 must be positioned in, such thatthe positioning block 10,110 will be positioned in a chosen positionrelative to the femur 39, when the positioning block 10,110 is engagedthereto. For example, when the shoulder 27 of the polyaxial screw 25reaches the correct position, the CAS display indicates that the screwhas been inserted to the precise depth required for the proximal face ofthe positioning block 10,110, when engaged on the polyaxial screw 25, toabut the most distal point of the femur 39. The positioning block 10,110can the be snapped onto the head 31 of the polyaxial screw 25, androtatably adjusted as described above. This permits the translation ofthe positioning block 10,110 relative to the femur 39 in theproximal-distal direction to be eliminated if required.

The distal pin drill guide assembly 50 as shown in FIG. 5 a will now bedescribed in further detail. The distal pin drill guide assembly 50 canequally have a cutting guide slot, such that the guide assembly can beused as a distal cutting guide to resect bone from the condyles of thefemur prior to installation of a femoral implant. It is also to beunderstood that the guide block can be used as a drill guide forcreating other holes than those for locating pins for a distal cuttingblock used in the femoral preparation for a implant in knee replacementsurgery. Additionally, while the distal pin drill guide assembly 50 isintended for use with the positioning block 10 in total knee replacementsurgery, an equivalent structure can also be used for any surgicalapplication where one moveable element must be precisely translated aselected distance relative to another fixed element.

Referring now to FIG. 15, the surgical tool guide 50, particularly adistal pin drill guide assembly in the preferred embodiment, comprises aguide block 52 and a anterior guiding platform 54. The drill/cuttingguide block 52 comprises a central slot 78 for receiving the tongueportion 80 of the guiding platform 54, such that the guide block istranslatable along the tongue portion 80, thereby permitting relativedisplacement therebetween. The anterior guiding platform 54 comprisesfixation pegs 82, which in the preferred embodiment, are adapted forengagement with the universal positioning block 10 fixed directly to thefemur, generally intramedullary mounted thereto using a polyaxial orstandard bone screw, or another similar fixation method. In this case,the drill/cutting guide block 52 is enabled to slide in theproximal-distal direction, over the anterior surface of the distal endof the femur.

As seen in FIGS. 16 a, 16 b and 17 a, the guide block 52 comprises abiased locking mechanism 56, used to locate the guide block 52 on theguiding platform 54, which generally includes an outwardly biased,semi-captive plunger 58 which fits within a transversely alignedcylindrical socket 60 in the guide block. The blind socket 60 comprisesa first open end 62 in one side of the guide block and a blind secondend 64. A blade spring 66, preferably integrally formed in the guideblock by machining two parallel axially aligned slots 67 therein,intersects the socket 60 near the second end 64 thereof. The plunger 58,best seen in FIG. 17 b, is therefore the only discrete element of themechanism, and comprises an outer end 70, an inner end 68, a locatingpin 72 radially projecting from the substantially cylindrical plunger ata point therebetween, and a central inner flat slot portion 74 formedthrough one edge of the plunger and corresponding to the slot 78 formedthrough the guide block. A pawl 76 is integrally formed in the plungersuch that the point projects into the slot 74 of the plunger.

Referring to FIGS. 17 a, 17 b and 17 c, the plunger 58 is inserted intothe socket 60 by aligning the pin 72 with a transverse pin slot 75disposed along a front side of the guide block, once the pin blocks anyfurther transverse movement of the plunger, the pin 72 can pass throughaxially directed slot 77 which joins the side transverse slot with a toptransverse slot 73, such that the plunger can be rotated ninety degrees.The alignment pin 72, which is retained within the transverse top pinslot 73, thereby limits the transverse movement of the plunger as itslides within the socket 60 of the guide block. As the blade spring 66forces the plunger 58 outwards, the pin 72 can not readily slide out ofthe top pin slot 73. The plunger is therefore securely retained withinthe socket. However, removal of the plunger from the socket, whenrequired, is nevertheless a simple and quick procedure. The outer end 70of the plunger 58 is depressed enough such that the alignment pin 72 isadjacent the axially directed top slot 77, perpendicular to the toptransverse slot 73. The plunger is then rotated about itselfapproximately ninety degrees, such that the pin passes through the slot77 and into the front transverse pin slot 75 which horizontally extendsbetween the vertical slot 77 and the edge of the block. The plunger 58can then be completely slid out of the socket 60.

This pin and slot engagement system therefor permits easy installationand removal of the plunger within the guide block, while neverthelesssecurely retaining the plunger therewithin and limiting its movement byproviding inner and outer stops. The inner end 68 of the plunger engagesthe blade spring 66, such that the blade spring provides a spring forceagainst the plunger, biasing it outwards. When the plunger is installedin position within the socket, the plunger is normally biased outwardlysuch that the pin 72 is at the outer end of the slot 73 and the pawl 76projects into the slot 78 of the guide block, as shown in FIG. 16 a. Thepawl 76 engages notches 84 disposed along one edge of the tongue 80 ofthe anterior guiding platform 54 when it protrudes into the slot 78 ofthe guide block through which the tongue 80 passes. This prevents anymovement of the guide block 52 on the guiding platform 54. When theouter end 70, of the plunger 58, that protrudes beyond the edge of theguide block is depressed, thereby acting against the blade spring 66,the pawl 76 of the plunger is retracted into the socket such that it nolonger projects into the slot 78 of the guide block and therefore intothe notches 84. As long as the outer end of the plunger is depressed, asshown in FIG. 16 b, the guide block 52 is permitted to slide along thetongue 80 of the guiding platform 54. However, as soon as the end of theplunger is release, the blade spring forces the pawl portion 76 of theplunger back into one of the notches 84. The blade spring thereforenormally retains the pawl engaged in a notch 84, such that the guideblock 52 is retained in place on the guiding platform 54.

Referring to FIG. 18, the locating pegs 82 of the anterior guidingplatform 54 are preferably engageable with corresponding holes 40 in theuniversal positioning block 10. As described above, the positioningblock 10 is aligned in a plane parallel the distal cut to be made, andsecured in place. With the positioning block in a known referenceposition relative to the most distal end of the femur, the exactdistance that the distal drill/guide block 52 must be displaced alongthe anterior guiding platform 54 such that the correct amount of bone isresected by the distal cut is determinable. Preferably, the positioningblock is directly abutted the most distal femoral condyle. The guideblock 52 can then be located at a position along the anterior guidingplatform, based on the type of implant being used, such that the pindrill holes or cut made using the guide block 52 are accuratelypositioned. The proximal-distal displacement of the guide block 52 onthe anterior guiding platform 54 permitted by the disengageable lockingmechanism 56, enables distal cuts of various resection amounts to bemade as required. This femoral distal resection amount can vary as afunction of the type of implant being used, or the specific anatomicalstructure of the patient. A plurality of graduations are provided alongthe tongue 80, preferably at 1 mm intervals. This permits accuratedetermination of the distance that the guide block is moved relative tothe fixed positioning reference block. The same intervals alsopreferably correspond to the distance between each adjacent notch 84.

If the positioning block 10 is being used in conventional (i.e.:non-CAS) surgery, it does not require a trackable member 16, andtherefore can be used as depicted in FIG. 5 a. If the position relativeto the bone, into which the positioning block 10 is aligned and fixed,is known or can be determined, then the distal drill/cutting guide block52 can be displaced the required amount on the tongue 80 of the platform54 relative to the fixed positioning block 10, thereby permitting drillholes or the distal cut to be created in the required locations.

While the drill/cutting guide block 52 of the surgical tool guide 50 canbe used to create a distal cut in the femur as required for installationof an implant, the positioning block 10 of the present invention canalso be used with standard cutting blocks or jigs typically used toperform the cuts required for the installation of a particular implanttype. Various different knee replacement implants are currently used.Generally, each implant type requires cutting guide blocks, used tocreate the distal and the anterior cuts in the femur and the tibial cut,which are specific to that particular implant. Accordingly, allreference guides used to correctly position the cutting guide blocks andCAS navigation systems have traditionally had to be either tailored toone specific implant type or had to include a plurality of adapters,each able to accommodate one implant-specific cutting guide block. Usingeither one of a universal distal cut adaptor and a universal anteriorcut adapter, the positioning block 10 of the present invention, guidedby the CAS total knee replacement system as described herein, can beused to position the distal and anterior cutting guide blocks of anyimplant type in the necessary position. Therefore, this permits kneenavigation surgeries with any implant brand or cutting guide block typeusing the same instruments and the same CAS system.

The common element in all knee cutting jigs or guide blocks produced bythe various implant manufacturers is the cutting reference surface usedto guide the saw blade. Accordingly, the universal adapters of thepresent invention comprise a plate portion adapted to mate with the sawguide slot on any typical knee surgery cutting guide block.

Particularly, referring to FIG. 19, the universal distal cutting guideadaptor 350 is mounted to the positioning block 10 as described above.The universal distal cutting guide adaptor 350 engages a standard distalcutting guide block 352 corresponding to a given implant type, and isadapted to position the standard distal cutting guide block 352 in adesired location to make the distal resection of the femoral condyles.The universal distal cutting guide adaptor 350 comprises generally aplate portion 354 which is shaped to fit within the saw blade guideslots in most standard distal knee cutting guide blocks currently usedin total knee replacement surgery. Two plate engaging posts 356 arefixed to the plate portion 354 at their proximal ends and extendgenerally perpendicularly therefrom. The distal ends of the plateengaging posts 356 mate with a plate positioning member 360, which isengaged to the positioning block 10 and which permits the plate portion354 to be moved proximally or distally to be positioned at a givenoffset from the proximal reference surface on the positioning block 10.The plate positioning member 360 preferably permits predeterminedincremental translation of the plate engaging posts 356 relativethereto. The plat positioning member 360 can therefore comprise a rackand pinion type mechanism, or a biased rack and pawl mechanism asdescribed above with regards to the surgical tool guide 50.

Once the plate portion 354 is positioned at the predetermined locationrelative to the positioning block 10 using the plate positioning member360, it can be tracked by the CAS system which is tracked thepositioning block 10. The reference surface on the positioning block 10can then be abutted against the femur, and the tracked plate portion 354is accordingly then already positioned at the predetermined distal cutlocation required by the implant type being used. The standard distalcutting guide block 352 is then simply slid overtop of the plate portion354 which inserts into the saw guide slot therein. The standard distalcutting guide block 352 can then be pinned in place on the femur. Oncethe standard distal cutting guide block 352 has thus been correctlypositioned and pinned in place, the positioning block 10 and theuniversal distal cutting guide adaptor 350 attached thereto canaccordingly be completely removed from the femur and the distal cut canthen be made. This applies regardless of the type of standard distalcutting guide block 352 used, or the amount of resection required by thetype of implant chosen.

Referring to FIGS. 20 a and 20 b, the universal anterior cutting guideadaptor 380 is similarly engaged to the top face of the positioningblock 10, and used to locate a standard anterior cutting guide block 382as shown in FIG. 20 b. The universal anterior cutting guide adaptor 380comprises a plate portion 384 which is fixed to the top of thepositioning block 10 by thumb screws 388, the plate portion being sizedto fit within the saw blade guide slot in most standard anterior cuttingguide blocks 382. Accordingly, the location of the plate portion 384will correspond to the location of the anterior cut made in the femur.As the plate portion 384 can be tracked by the CAS system because it isfixed in place on the tracked positioning block 10, the location of theanterior cut can be carefully aligned. The universal anterior cuttingguide adaptor 380 also further includes a triangularly shaped blockportion 386 which is adapted to be securely pinned in place on theanterior surface of the femur. Therefore, once the positioning block islocated in the desired location to align the plate portion 384 asrequired, the block portion 386 can be pinned in place on the femur. Thepositioning block 10 and the universal anterior cutting guide adaptor380 can then be completely removed, leaving only the universal anteriorcutting guide adaptor 380 pinned in place on the femur, the plateportion 384 thereof being positioned exactly where the anterior cut isto be made. The standard anterior cutting guide block 382 correspondingto the particular implant being used is then simply slid onto the plateportion 384 of the universal anterior cutting guide adaptor 380, andpinned in place as shown in FIG. 20 b. The universal anterior cuttingguide adaptor 380 can then be removed from the femur, and the anteriorcut can then be made.

The embodiments of the invention described above are intended to beexemplary only. The scope of the invention is therefore intended to belimited solely by the scope of the appended claims.

The invention claimed is:
 1. A positioning block for use in knee surgerycomprising: a rotational mounting element being removably engageable toa substrate surface by a multi-axial fastener such that the rotationalmounting element is selectively rotatable relative to the substratesurface about at least two substantially perpendicular axes of rotation;a guide body portion being engaged with the rotational mounting elementsuch that the guide body portion is translatable relative thereto alongat least a proximal-distal axis, while being rotationally fixed relativeto the rotational mounting element such that the guide body portion andthe rotational mounting element rotate together relative to thesubstrate surface, and wherein the guide body portion is therebymoveable relative to the substrate surface in at least three degrees offreedom, the three degrees of freedom including at least two rotationaldegrees of freedom and at least one translational degree of freedom; anda trackable member fastened to the guide body portion, the trackingmember being identified and tracked in three dimensional space by acomputer assisted surgical system such as to determine at least anorientation and movement of the guide body portion in three dimensionalspace.
 2. The positioning block as defined in claim 1, wherein the tworotational degrees of freedom comprise rotation in flexion-extension andvarus-valgus planes.
 3. The positioning block as defined in claim 1,wherein the positioning block permits at least four degrees-of-freedommovement relative to a bone element to which it is fixed.
 4. The,positioning block as defined in claim 3, wherein the guide body portionis engaged with the rotational mounting element such that it is alsotranslatable relative thereto along an anterior posterior axis.
 5. Thepositioning block as defined in claim 3, wherein the at least fourdegrees-of-freedom comprise two rotational and two translational degreesof freedom.
 6. The positioning block as defined in claim 1, wherein themulti-axial fastener is a bi-axial fastener providing two rotationaldegrees of freedom.
 7. The positioning block as defined in claim 1,wherein the computer assisted surgical system further identifies andtracks a position of the trackable member in three dimensional space inaddition to said orientation thereof.
 8. The positioning block asdefined in claim 1, wherein the guide body portion includes a surgicaltool guide block.
 9. The positioning block as defined in claim 8,wherein the surgical tool guide block is positionable at a fixeddistance relative to the positioning block.
 10. The positioning block asdefined in claim 8, wherein the surgical tool guide block comprises auniversal adaptor for locating standard cutting guide blocks used intotal knee replacement surgery.
 11. The positioning block as defined inclaim 8, wherein the surgical tool guide block comprises at least one ofa drill guide hole and a distal cutting guide slot.
 12. The positioningblock as defined in claim 8, wherein the surgical tool guide block isdisplaceable on a platform engaged to the rotational mounting elementand which provides support for the surgical tool guide block such thatsliding displacement of the surgical tool guide block thereon ispermitted.
 13. The positioning block as defined in claim 1, wherein thepositioning block has substantially seamless surfaces that are at leastone of substantially exposed or exposable, such that the surfaces areeasily pressure cleaned and autoclaved to remove biological mattertherefrom.
 14. The positioning block as defined in claim 1, furthercomprising at least one of a cutting and a drilling guide portionintegrally incorporated with the guide body portion.
 15. The positioningblock as defined in claim 1, wherein at least two of said threedegrees-of-freedom are independently adjustable relative to the boneelement, the guide body portion being adjustably engaged to therotational mounting element such that selective displacement of theguide body portion in each of the at least two rotational degrees offreedom relative to the bone element is permitted independently.
 16. Thepositioning block as defined in claim 15, further comprising at leasttwo independent adjustment mechanisms, each being adjustable insubstantial isolation for respectively displacing the guide body portionin one of the at least two rotational degrees of freedom such as topermit independent rotation in the flexion-extension and varus-valgusplanes, thereby enabling the cutting tool to be disposed in at least thedesired orientation.
 17. The positioning block as defined in claim 3,wherein said at least four degrees-of-freedom comprise two rotationaldegrees-of-freedom and two translational degrees-of-freedom.
 18. Thepositioning block as defined in claim 5, wherein the guide body portionis selectively translatable in the two translational degrees-of-freedomalong two perpendicular axes relative to the rotational mountingelement.
 19. The positioning block as defined in claim 1, furthercomprising a display in communication with the computer assistedsurgical system for indicating when the orientation of the positioningblock relative to the bone element corresponds to a desired orientationrequired to perform a predetermined cut in the bone element.
 20. Thepositioning block as defined in claim 12, further comprising a displayin communication with the computer assisted surgical system forindicating an exact location on said platform at which the surgical toolguide block is to be fixed such that the surgical tool guide block islocated in a selected position thereon relative to the bone element.